1. Field of the Invention
The invention pertains to the manufacture of spools and reels generally, and more particularly to plastic spools and reels for receiving electrical wire and cable during manufacture and for subsequent handling, storage and dispensing thereof.
2. State of the Art
Stranded materials, upon manufacture, are typically taken up directly onto a reel or spool. The take-up spool or reel receives the strand directly from the last step in the manufacturing process. Thereafter, the filled spool is effective for storage and handling purposes. Upon sale or distribution, the spool is often placed on an arbor, either alone or with other spools, for convenient dispensing of the linear or stranded material. Linear or stranded materials include electrical wire whether in single or multiple strands and cable (comprised of multiple wires), rope, wire rope, hose, tubing, chain and plastic and rubber profile material (generally any polymeric or elastomeric extruded flexible material). In general, a host of elongate materials as diverse as pharmaceutical unit dose packages, fiberoptic line and log chains are stored on spools. Likewise, ribbon, thread and other stranded materials are wrapped on spools.
The requirement for a spool in the manufacture and handling of wire is substantially different than spools in the textile industry. For example, the weight of wire is several times the weight of thread or rope. The bulk of wire, which translates to the inverse of density, is substantially lower for wire than for hose, tubing or even chain.
Meanwhile, most spools are typically launched on a one way trip. The collection and recycling of spools is hardly worth the effort, considering that their materials are not easily recyclable.
In the art, a typical spool has a tube portion extending between two flange portions positioned at either end of the tube portion. For example, one tube has a standard 2-inch outside diameter piece while the flanges conventionally have a 61/2-inch outside diameter. Typically, a spool has a rounded rim or rolled edge at the outermost diameter. This rim serves structural as well as aesthetic and safety purposes. Spools may be manufactured in a variety of tube lengths and thus are typically manufactured as three-piece units. That is, the tube is a molded, or preferably extruded, piece. The tube can be cut to length from standard extruded stock. Each flange has an insertion portion, which is fitted inside one end of the tube and there bonded.
As a result of the requirement for bonding, most plastic spools known in the art are manufactured of polystyrene or acrylonitrile-butadiene-styrene (ABS). Although the impact performance of styrene is rather poor, ABS is substantially better. A variety of well known solvents can be used to bond styrene-based polymers. Also given the structural and cost requirements, the amount of plastic in a spool dictates inexpensive styrene-based plastics.
Olefinic plastics, including polyethylene, polymethylpentene, polybutadiene, polypropylene and the like cannot be bonded with solvents. As a result, the multi-piece spools known in the art do not use polyolefins, also called olefinic plastics, olefin polymers or polyolefins.
A spool of wire 61/2 inches in diameter may weigh twenty pounds. A spool or reel 12 inches in diameter may weigh over a hundred pounds. The impact load (standard impact test or drop test) of a full (e.g. weighing approximately twenty-pound) spool of wire dropping from a bench or other work surface (e.g. a counter accessible to a seated or standing worker, as known in the art) to a floor in a manufacturing environment (e.g. typically concrete, wood blocks, or other hard surface, as known in the art) is sufficient to fracture the spool in any of several places, releasing the wire in a tangled, useless mass. This exercise is typically used as a standard drop test, as known in the art.
Spools may break at the corner where the tube portion meets the flange portion or may fracture at an engagement portion along the tube portion. Three-piece spools typically break near the corner between the flange and the tube portion where a joint bonds the tube portion to the flange portion.
Because multi-piece spools often break at the joints, applicant developed the two-piece polystyrene spool having a two-inch outside diameter for the tube and a 1/2 inch engagement length on a single step. The step is formed on each mating half of the spool, each half comprising a flange on a tube portion. The step is essentially formed with a right angle shoulder. Each of the edges on the inside and outside right angles forming the axial ends of the step is broken. A broken edge indicates that the burr is removed from exterior corners of tooling and the internal corners are chamfered slightly to prevent a burr on a finished part. A broken edge is cut approximately 0.005 inches on an edge of the chamfer or fillet as appropriate.
Each step, male and female, has a wall thickness of half the thickness of the wall thickness of the tube. The two-piece spool employs a first half comprising a flange portion and a tube portion assembled with a second half comprising a second flange portion and a second tube portion. The first half is made to receive the second half along an engagement area. A step on the male half of the spool and a step inside the female half of the spool allow a matched fit which can be solidly bonded. The joint is typically located such that the break in the outside surface appears at the middle of the resulting tube length. The joint is thus located at a maximum distance from the flange.
A three-piece spool is the industry standard for spools of 61/2-inch diameter. The typical length of the engagement portion on each end is approximately one eighth to one quarter of an inch. Nevertheless, the two-piece spools having half-inch engagement length still experience some breakage during drop tests when manufactured in styrene or styrene-based plastics such as ABS.
Polyolefins are very tough materials. Tough means that a material can tolerate a relatively large amount of straining or stretching before rupture. By contrast, a material which is not tough will usually fracture rather than stretch extensively. As a result, when a reel of wire is dropped, the energy of impact breaks the spool. Polyolefins, by contrast, may actually be drawn past yielding into their plastic elongation region on a stress-strain chart. Polyolefins thus elongate a substantial distance. The result is that olefinic plastics will absorb a tremendous amount of energy locally without rupture. Thus, the wire on a spool which has been dropped does not become a tangled mat of loops.
Given their toughness, olefinic parts will bend, strain, distort, but usually not break. Nevertheless, olefinic plastics are not typical in the art of wire spools. Polyolefin parts are not bonded into multi-piece spools, however. Lack of a solvent is one problem, lack of a durable adhesive is another. Therefore, any spool would have to be manufactured as unit of a specific size. The inventory management problem created by unique spools of various sizes is untenable. Although the cost of some olefinic resins is lower than that of styrene-based resins. Moreover, the cycle time of molds directly related to material properties is usually much faster for styrene-based resins. The designs available use wall thicknesses which result in warpage as well. All these factors and more combine to leave olefinic resins largely unused in the spool industry, as is the design of bonded parts for spools from olefinic resins.
What is needed is a small diameter (typically 61/2-inch outside diameter) plastic spool, which can tolerate the energy of being dropped when fully wrapped with wire. In addition, even in the standard styrene-based plastic spools, a better tube design than the single step type is desired. In drop tests, a spool may be dropped axially, radially or canted off-axis. In a radial drop, spools that break typically fail near the middle of the length of the tube. In axial drops, flanges may separate from tubes in failed spools. In an off-axis drop, flanges typically fracture.
Large spools are typically called reels in the wire industry. Heavy-duty reels of 12 inches in diameter and greater (6 feet and 8 feet are common) are often made of wood or metal. Plastic spools of 12-inch diameter and greater are rare and tend to be very complex. The rationale is simple. Inexpensive plastics are not sufficiently strong to tolerate even ordinary use with such a large mass of wire or cable wrapped around the spool.
Moreover, large flanges for reels are very difficult to manufacture. Likewise, the additional manufacturing cost of large spools is problematic. High speed molding requires quick removal after a short cycle time. Flanges are typically manufactured to have very thick walls. Increased thicknesses directly lengthen cycle times. Thus designs do not scale up. Therefore, the flanges have very slow cooling times and molding machines have low productivity in producing them.
Styrene plastic is degraded by recycling. That is, once styrene has been injection molded, the mechanical properties of the resulting plastic are degraded. Thus, if a spool is recycled, ground up into chunks or beads and re-extruded as part of another batch, the degradation in quality can be substantial. Olefinic plastics improve over styrene-based plastics in that olefinic plastics can be completely recyclable. The mechanical properties of an olefinic plastic are virtually identical for reground stock as for virgin stock.
In reels, a 12-inch diameter unit is instructive. Such a spool is usually manufactured of wood. Nevertheless, a plastic spool in 12-inch diameter may also be manufactured with a pair of plastic flanges holding a layered cardboard (paperboard) tube detained therebetween. The flanges are typically bolted together axially to hold the tube within or without a circumferential detent as with wooden reels.
The reels have an additional difficulty when they are dropped during use. The flanges do not stay secured. One difficulty with the structural integrity of the three-piece reel design is that the tube is not fastened to the flange. The flange and tube are often precarious wooden assemblies held together by three or more axial bolts compressing the flanges together. The tube is prone to slip with respect to the flanges, breaking, tilting or otherwise losing its integrity under excessive loads. Such loads result from the impact of dropping onto a floor from a bench height or less. Standard benches, or workbenches, are known in the art to be built at heights ranging from near a seat height, to a height accessible only to a standing worker. For the largest reels, rolling over or into obstacles or from decks during handling is more likely to be the cause of damage.
Very large cables, having an outside diameter up to several inches is taken up during manufacturing on a very large reel, from two feet to eight feet in diameter. The current state of the art dictates wooden reels comprised of flanges capturing a barrel-like tube of longitudinal slats therebetween. The two flanges are held together by a plurality of long bolts extending therethrough. Wooden reels are not typically recyclable. A splinter or blemish in a reel can damage insulation on new cable or wire wrapped therearound at the manufacturing plant. Damaged insulation destroys much of the value of a reel of cable or wire. That is, the wire must be spliced, or may have damage extending over several wrapped layers of wire. Splices segmenting the original length of wire wrapped on the reel add costs in labor, reliability, service and the like.
Wood cannot be recycled and reconstructed cost effectively. In addition, the plurality of bolts and nails must be removed with other related metal hardware. The reels do not effectively burn without the labor investment of this dismantling operation.
Also, a wooden reel that is slightly out of adjustment, damaged, or broken, is problematic. A broken reel leaves a large area splintered to damage wire insulation. A reel which is loose will tilt and twist as the slats shift with respect to the flanges.
Steel reels tend to be more frequently recyclable. However, each must be returned in its original form to be reused. Thus, the bulk of transfer is as large as the bulk of original shipment, although the weight is less. Also, steel is heavy, subject to damage by the environment such as by stains, rust, peeling of paint, denting, accumulation of coatings or creation of small burrs on surfaces and corners. For example, when a reel is rolled over a hard surface, sharp objects, grit or rocks tend to raise small burrs on the outer edge of the flange. Similarly, contact with any sharp or hard object can raise burrs on the inside surfaces of the flanges.
As with wooden reels, only to a greater extent, a burr on a steel reel tends to act like a knife, slicing through insulation and ruining wire. Perhaps the most difficult aspect of burrs is that they are hardly detectable at sizes which are nevertheless highly damaging to insulation. Of course the weight and cost of steel reels is another factor in the difficulty of employing them for delivery of cable.
What is needed in large reels of from a foot to eight feet approximately in outside flange diameter is a reel which is dimensionally stable, maintains structural integrity in service and during accidental dropping, which will not fracture or separate at a flange if it is dropped, and which is economically recyclable. In a large reel, on the order of two to eight feet in diameter, what is needed is a lightweight, high-strength reel. The reel should not tend to damage wire when scratched, gouged, or otherwise having a burr raised on any key surface. Similarly, a large reel should be resilient enough that it does not maintain a permanent set, such as a steel reel will, when damaged. A plastic reel should be formed of a material which is tough. The material should be flexible enough that a burr will not damage insulation. Finally, a large reel should be recyclable. Recycling is most efficient if a reel can be reground near the site of use. Empty reels are more voluminous than they are heavy.